The present invention relates to a device for rotating a vector waveform in a vector waveform display of a vector scope, and more particularly to a device for rotating a demodulated color difference signals, which is employed instead of a phase shifter for shifting the phase of a regenerated sub-carrier.
FIG. 1 is a schematic block diagram of a conventional vector scope that displays the vector waveform of a composite video signal. As shown in FIG. 1, the conventional vector scope comprises input means 1, Y/C separation means 2, synchronizing separation means 3, sub-carrier regenerating means 4, a phase shifter, decoder means 8, and display means 11.
The input means 1 inputs a composite video signal, and outputs the signal to the Y/C separation means 2, the synchronizing separation means 3 and the sub-carrier regenerating means 4. The Y/C separation means 2 extracts a chrominance signal of the composite video signal from the input composite video signal, employing a filter such as a band pass filter, a comb filter and a three dimensional filter, and outputs the chrominance signal to the decoder means 8. The synchronizing separation means 3 extracts a composite synchronizing signal within a synchronizing signal part of the composite video signal from the input composite video signal, employing a negative peak detection circuit. Moreover, the synchronizing separation means 3 separates the composite synchronizing signal into a vertical synchronizing signal and a horizontal synchronizing signal, employing a stable multi-vibrator etc., and generates a burst gate signal based on the vertical and horizontal synchronizing signals to output the burst gate signal to the decoder means 8. The sub-carrier regenerating means 4 generates a sub-carrier signal synchronous with the burst signal from the input composite video signal, employing a PLL, and outputs the sub-carrier signal to the phase shift means 6 in the phase shifter.
The shift amount setting means 5 in the phase shifter sets up a phase shift amount (i.e., an amount for rotating the vector waveform displayed on the display means 11) from the sub-carrier signal input into the phase shift means 6 to the sub-carrier signal output to the phase shift means 6, and outputs the shift amount to the phase shift means 6. The phase shift means 6 shifts the phase of the input sub-carrier signal in accordance with the input phase shift amount, employing a variable phase circuit such as a goniometer, shifts the phase of the input sub-carrier signal, and outputs the sub-carrier signal with phase shifted to 90 degree phase shifting means 7 and the decoder 8. The 90 degree phase shifting means 7 in the phase shifter generates the sub-carrier signal orthogonal to the input sub-carrier signal, employing a 90 degree phase circuit, and outputs the generated signal to the decoder 8. The decoder 8 demodulates the chrominance signal input from the Y/C separation means 2 into color difference signals (an R-Y signal and a B-Y signal), employing the sub-carrier signal input from the phase shift means 6 and the sub-carrier signal input from the 90 degree phase shifting means 7 (i.e., sub-carrier signals orthogonal to each other), and outputs the color difference signals to the display means 11. The display means 11 displays the Lissajour figure with the B-Y signal of the input color difference signals as x axis and the R-Y signal as y axis.
One example of the conventional vector scope was disclosed in Japanese Patent Laid-Open No. 7-312762. The vector scope as described in Japanese Patent Laid-Open No. 7-312762 comprises the improved phase shifter.
[Patent document 1]
Japanese Patent Laid-Open No. 7-312762 (page 3, paragraph 2)